Solenoid devices that use their encasement in magnetic circuits are widely known. An exemplary version is illustrated in U.S. Pat. No. 4,004,258 Arnold wherein the encasement 12 serves as a component of two magnetic circuits 19,21. Such devices are particularly useful as valve actuators in applications which demand a latching function. A problem in such applications is that if electrical power is lost in the system used to excite the coils of the solenoid device, the position of the armature (and, by extension, the position of the valve) is fixed and cannot easily be changed without restoration of power.
The '960 application solves the above-described problem by providing a solenoid encasement with variable magnetic reluctance. In the species illustrated in the '960 application, reluctance is varied by rotational movement of a portion of the encasement. The rotational movement effects linear movement of an associated valve stem from one latched position to another. The illustrated species is unnecessarily complicated in design, and relatively expensive to manufacture. The present invention is directed to providing a species of simpler design and lower cost. Other advantages of the invention may become apparent from the following description, which includes the appended claims and accompanying drawings.